The Mask + Heart is a new enemy added in the Wrath of the Lamb expansion. They are commonly found in Necropolis and are found less commonly in Utero. Hearts may be found on their own in Utero.

It consists of an invulnerable mask, which uses a movement pattern similar to a Knight, and a slow moving heart that will shoot projectiles in the cardinal directions when the player approaches it. The Mask itself is vulnerable to The Necronomicon.

A boss variant called the Mask of Infamy can be encountered in the first floor in Necropolis. She has a similar mechanic to this enemy. However, the heart will shoot in eight directions and the Mask will not die with the Heart, but continue to fight until it is destroyed by repeatedly shooting its backside.

Despite both the Hearts and the Masks being able to float, they cannot float over rocks and pits.